Bioavailability of vitamin D assessed by a competitive-protein binding 250HD assay revealed that oil-depot-S.C. and I-M injection of vitamin D resulted in delayed serum 250HD rises compared to PI and IV dosing. A sensitive carboxy-terminal radio-immunoassay for parathyroid hormone was developed and used to demonstrate acute as well as chronic changes in hormone secretion. Clinical, laboratory and genetic investigations of a large kindred with hypophosphatasia demonstrated that hypophosphatasic children were capable of normal bone remodeling and growth and that the increments in urinary phosphoethanolamine and phosphoserine were the result of disordered hepatic and not skeletal alkaline phosphatase metabolism. A prospective study of 110 women with osteoporosis and the "crush fracture syndrome" revealed a heterogeneous population defined histologically (bone biopsy following tetracycline labeling) as either "active" or "inactive" osteopenia. NaF therapy of patients with the inactive form proved effective in stimulating new (and normal) collagen formation and its subsequent mineralization. Two thermalabile proteins were isolated from bovine hypothalamic tissue which induced hypocalcemia in intact but not thyroparathyroidectomized rats. Accumulated observations suggest a CNS control of calcitonin release in the rat.